The present invention relates to a tandem-type image forming apparatus in which image forming stations for respective colors are arranged along a transfer belt, each image forming station being composed of an image carrier, a charging means and a developing means which are arranged around the image carrier. The image forming apparatus forms a multi-color image by passing the transfer belt through every station.
Tandem-type image forming apparatuses as described above are categorized into two types as:
(1) an apparatus employing a paper delivery method which comprises a plurality of image forming stations arranged in an array, in which a receiving medium is electrostatically attracted to a delivery belt and is carried to be brought in contact with the respective stations in order and electrostatic transferring force is applied between each station and the recording medium, thereby superposing toner images of plural colors while directly transferring the toner images to the receiving medium; and
(2) an apparatus employing an intermediate transfer method which comprises a plurality of image forming stations arranged in an array, in which an intermediate transfer belt made of a dielectric substance is carried to be brought in contact with the respective stations and electrostatic transferring force is applied between each station and the intermediate transfer belt so as to transfer primarily toner images of the respective stations one by one to superpose the toner images on the intermediate transfer belt and the superposed toner images are transferred secondarily from the intermediate transfer belt to a recording medium at once.
In the aforementioned paper delivery method, it is required to provide a means (roller or brush) for attracting the receiving medium to the delivery belt and high voltage power supply. In the intermediate transfer method, however, such a means and high voltage power supply are not required. Further, in the paper delivery method, it is required to strictly control the transfer bias to be applied to respective image transferred portion according to the size, the thickness, and the kind of the receiving medium. In the intermediate transfer method, the primary transfer of toner images is conducted to the intermediate transfer belt of which resistance, thickness, and surface roughness are constant regardless of the aforementioned factors of the receiving medium. The control of the transfer condition including the transfer voltage or transfer current and contact pressure must be conducted only for the secondary transfer of the toner images to the receiving medium. Therefore, the intermediate transfer method has a lot of advantages.
On the other hand, the apparatus can also be categorized according to the arrangement of the respective image forming stations. There are a method of arranging the stations horizontally and a method of arranging the stations vertically. The former has a disadvantage of requiring a larger area for placing, while the latter has a disadvantage of making the apparatus too tall to be put on a desk.
Therefore, a method of arranging the respective image forming stations obliquely is conventionally known as disclosed in Japanese Patent Unexamined Publication No. H11-95520 and Japanese Patent Unexamined Publication No. H8-305115.
However, this method has a disadvantage as follows. Since the image forming stations are arranged at an upper portion of a belt, which may be either the receiving medium delivery belt or the intermediate transfer belt, obliquely disposed, toner may spill from developing means of each image forming station so as to stain image forming means such as the belt, thereby deteriorating the image quality. In addition, an exposure means must be located at an upper portion of the apparatus, thereby increasing the vibration of the apparatus and thus also deteriorating the image quality.
The first object of the present invention is to provide an image forming apparatus, capable of resolving the aforementioned conventional problems, which comprises respective image forming stations arranged obliquely and can prevent image forming means such as a belt from being stained by spilled toner and also reducing the vibration of an exposure means.
Whether the image forming stations are arranged vertically or obliquely, the important matter is the position of a fixing device in order to make the apparatus compact. This is because the image quality is deteriorated when the heat and/or vibration generated from the fixing device is transmitted to the exposure means, the transfer belt, and the image forming means. It is also important to allow easy maintenance of the fixing device and easy removal of a jammed paper sheet around the fixing device. It is still also important to allow easy removal of a jammed paper sheet around the transfer belt and easy replacement of consumables such as the image carriers and the developing means. For this, Japanese Patent Unexamined Publication No. 2001-142378 discloses an apparatus in which a transfer belt is pivotally moved outside of the apparatus to allow replacement of consumables. However, this apparatus has a problem that it is impossible to replace the developing means alone, a problem of toner scattering, and a problem that it is difficult to maintain the fixing device itself and difficult to remove a jammed paper sheet around the transfer belt or around the fixing device.
Therefore, the second object of the present invention is to provide an image forming apparatus, capable of resolving the aforementioned conventional problems, which comprises respective image forming stations arranged obliquely or vertically, allows easy replacement of consumables, facilitates the maintenance of a developing means and a fixing device itself, and facilitates the removal of jammed paper sheets from near a transfer belt or around the fixing device.
For achieving the aforementioned first object, the present invention provides an image forming apparatus of a tandem type comprising image forming stations for respective colors arranged along a transfer belt, each image forming station including an image carrier, a charging means and a developing means disposed around said image carrier, wherein the transfer belt is passed through the respective image forming stations, thereby forming a multi-color image, and said image forming apparatus being characterized in that said transfer belt is laid around the driving roller and the driven roller with a constant tension, one of the driving roller and the driven roller is positioned obliquely above the other roller, the driving roller and the driven roller are disposed such that the belt tension side at the time of driving the transfer belt is on the lower side, and the image carriers of the respective image forming stations are in contact with the belt tension side.
According to this arrangement, the transfer belt and the exposure means are prevented from being stained by spilled toner and the vibration of the exposure means is reduced. In addition, the fixing means can be arranged in a space formed obliquely above the components in the apparatus, thereby enabling the reduction in heat transfer to the exposure means, the transfer belt, and the image forming means and lessening the frequency of taking the action for correcting color registration error.
For achieving the aforementioned second object, the present invention provides an image forming apparatus comprising image forming stations for respective colors arranged along a transfer belt, each image forming station including an image carrier, a charging means and a developing means disposed around said image carrier, wherein the transfer belt and the respective image forming stations are arranged obliquely or vertically, said image forming apparatus being characterized by further comprising: a housing body in which said respective image forming stations and the transfer belt are arranged; and a first movable section and a second movable section which are attached to said housing body such that the first and second movable sections are pivotally movable relative to said housing body, wherein a paper handling means and a fixing means are located in said first movable section and at least one of developing means, image carriers, and the transfer belt is located in said second movable section.
According to the aforementioned arrangement, in the image forming apparatus in which the respective image forming stations are arranged obliquely or vertically, the easy replacement of consumables is allowed, and the easy maintenance of the fixing device and the easy removal of jammed paper around the transfer belt and about the fixing device are also allowed.